Hearing aid assemblies are well known to those skilled in the art. By way of illustration and not limitation, reference may be had to U.S. Pat. No. 6,228,020 (compliant hearing aid), U.S. Pat. No. 6,438,244 (hearing aid construction with electronic components encapsulated in soft polymeric body), U.S. Pat. No. 6,473,512 (apparatus and method for a custom, soft-solid hearing aid), U.S. Pat. No. 6,434,248 (soft hearing aid molding apparatus), U.S. Pat. No. 6,432,247 (method of manufacturing a soft hearing aid), the references cited during the prosecution of the aforementioned United States patents, and the like. The entire disclosure of each of these United States patents, and of each of the references cited during their prosecution, is hereby incorporated by reference into this specification. Some of the teachings of these “prior art” patents are discussed below.
Major strides have been made in the hearing aid industry in the programmable digital signal processing systems. Hearing care professionals expected these advancements to solve the problematic issues of traditional sound amplification and thus advance the market forward. Unfortunately, these expectations have not been fully realized. These developments have solved many of the problems associated with traditional electronic design.
Historically, custom molded ear worn hearing instruments have been limited to an “acrylic pour” process as the means of construction. The development of computer chip microminiaturization and the development of computer chip programming, the ear worn instruments have become smaller.
Developments outside the hearing aid industry have resulted in a more advanced level of microminiaturization of electronic components for industrial applications. Thus, advanced signal processing can be housed in less volume than was necessary for the traditional electroacoustic components.
With the development of programmable hearing aids, using either analog or digital signal processing, custom electronic design has shifted from the manufacturing level to the clinical level. The hearing care professionals can now customize the acoustic system response using software control.
Advances have also been made in the custom prosthetic design and manufacture. In the late 1960's custom in the ear hearing aids were developed. The materials and techniques were adopted from the dental industry. The housing or shell is constructed with an acrylic ester copolymer that is hard. The shell housing hardness indexes or resistance to deformation is in the range of 90 Shore D scale. This is very hard. By comparison, a bowling ball has a hardness of about 90 Shore D scale. This process provides a structure that possesses the required strength and stiffness necessary to protect the sensitive electronic components mounted within the shell. Acrylic shells of in the canal hearing aids are positioned near the bony portion of the ear canal.
Digital production of customized hearing aids today replaces the labor intensive process with one that is fully computer driven. The hearing aids produced with this system typically offer a significantly better fit and therefore better performance than hearing aids produced using the techniques adopted from the dental industry.
The ear impression scanner is the point of entry of the digital hearing aid production system. The patient's ear impression is scanned using an optical scanning system. Laser planes are projected onto the ear impression. High-resolution cameras acquire images of the lines thus created on the ear impression. Image processing software tracks the images of the lines thus created on the ear impression.
The initial output of the scanning process is a point surface of approximately 200.000 points that is dependant on the impression. Surface creation software then optimizes this data and creates a polygonal model. The final surface is reduced to approximately 25,000 triangles. This results in an accurate replica of the full original impression in a compressed format, which makes it easy to manipulate, store and transfer.
Software creates a user defined shell thickness and optimally positions the electronic module, transducers and any controls. The ventilation and sound exit are then created. A milling path for the faceplate ensures a correct fit with the shell's geometry. Once the shell has been completed, it can be visualized inside the original impression to assess the fit with the user's ear. Deviations between the original impression and the finished shell can be displayed. The completed shell date is then imported to the 3D printing equipment. The printers use stereo lithography that uses a laser to solidify thin layers of a hypoallergenic UV cured acrylic liquid polymer. The shell is manufactured by the 3D printer.
The bony portion of the canal is extremely sensitive and intolerant of shells that are over sized or is in contact with the canal wall beyond the second anatomical bend. The rigid shell that does not compress pivots in reaction to jaw or head movement. This changes the direction of the receiver and transmitter yielding distorted acoustic response. In addition, the pivot action causes displacement of the device resulting in unwanted acoustic feedback. This problem has caused many shell modifications, thereby compromising the precision approach design process. Many such devices require some modification by the manufacturer. Most manufacturers can expect a high percentage of returns for modifications or repair within the first year. Thus, completely in the canal shell design has been reduced to more of a craft than science.
The current trend for custom hearing aid placement is to position the instrument toward the bony portion of the ear canal. The ear canal can be defined as the area extending from the concha to the tympanic membrane. It is important to note that the structure of this canal consists of elastic cartilage laterally, and porous bone medially. The cartilaginous portion constitutes the outer one third of the ear canal. The medial two-thirds of the ear canal is osseous or bony. The skin on the osseous canal, measuring only about 0.2 mm in thickness, is much thinner than that of the cartilaginous canal, which is 0.5 mm in thickness. The difference in thickness directly corresponds to the presence of apocrine (ceruminous) and sebaceous glands found only in the fibro-cartilaginous area of the canal. Thus, this thin-skinned thinly lined area of the bony canal is extremely sensitive to any hard foreign body, such as a hard shell hearing instrument.
Exacerbating the issue of placement of a hard foreign body into the osseous area of the canal is the ear canal's dynamic nature. It is geometrically altered by temporomandibular joint action and changes in head position. This causes an elliptical type of elongation (widening) of the ear canal. These alterations in canal shape vary widely from person to person. Canal motion makes it very difficult to achieve a comfortable, true acoustic seal with hard shell material. When the instrument is displaced by mandibular motion, a leakage or slit leak creates an open loop between the receiver and the microphone and relates directly to an electroacoustic distortion commonly known as feed back. Peripheral acoustic leakage is a complex resonator made up of many transient resonant cavities. These cavities are transient because they change with jaw motion as a function of time, resulting in impedance changes in the ear canal.
These transients compromise the electroacoustic performance of the hearing aid. The properties of the hard shells have limitations that require modification to the shell exterior to accommodate anatomical variants and the dynamic nature of the ear canal. The shell must be buffed and polished until comfort is acceptable. The peripheral acoustic leakage caused by these modifications results in acoustic feedback before sufficient amplification is attained.
Hollow shells used in today's hearing aid designs create internal or mechanical feedback pathways unique to each device. The resulting feedback requires electronic modifications to “tweak” the product to a compromised performance. With the industry's efforts to facilitate the fine tuning of the hearing instruments for desired acoustic performance, programmable devices were developed. The intent was to reduce the degree of compromise, but by their improved frequency spectrum the incidence of feedback was heightened. As a result, the industry still falls well short of audiological optimum.
A few manufacturers have attempted all soft, hollow shells as alternatives to the hard hollow shells. Unfortunately, soft vinyl materials shrink, discolor, and harden after a relatively short period of wear. Polyurethane has proven to provide a better acoustic seal than polyvinyl, but has an even shorter wear life. Silicones have long wear life but are difficult to bond with plastics such as acrylic, a necessary process for the construction of the custom hearing instruments. To date, acrylic has proven to be the only material with long term structural integrity. The fact remains, that the entire ear is a dynamic acoustic environment and is ill-served by a rigid material.
There are manufacturers constructing solid soft hearing instruments. The material is very soft, comprising an elastomer of about 3 to 55 durometer Shore A, and preferable 10 to 35 Shore A. The material can be a silicone polymer and it actually encapsulates the electronic components. This compliant type of hearing aid body solves many of the problems noted with the hard shell bodies. Unfortunately, fundamental electronic mounting problems result. The basic issue is the constant flexing of all of the very fine diameter interconnection wires from the micro miniature chip to the receiver, transmitter and face plate. The potential consequences are wire breakage and micro chip bond failure. The main cause of this constant flexing is the ear canal's dynamic nature. It is geometrically altered by temporomandibular joint action and changes in hear position. The electronic components are encapsulated and thus are forced to move with the soft body of the hearing aid. The result is a loss of reliability of the complex computer controlled system. The interconnection system must not be constantly flexed. The problem is further complicated by the necessary flexing whenever the instrument is inserted or removed from the patient's ear. The reliability of the bond between the soft silicone polymer and face plate is also questionable. The net result is a complex system that solves many of the problems associated with hard shell instruments but suffers from reliable system operation.
It is an object of this invention to provide a hearing aid assembly that is superior to the prior art hearing aid assemblies. By way of illustration and not limitation, some of the more particular objects of the invention are described below.
It is an object of this invention to provide an assembly that improves the performance and reliability of the hard shell acrylic ester copolymer hearing aid instruments or similar material and the solid soft hearing instruments. This is provided by incorporation of many of the unique advantages of both the hard shell and solid soft shell hearing aid instruments.
It is an object of this invention to provide a hearing aid assembly with one or more of the improved functions described below.
In one embodiment, a hypoallergenic UV cured acrylic shell hearing aid body (or similar material) is used, but the hearing aid body geometry for the right and left ear is modified by computer modeling to remove any portion of the shell that would interfere with the ear canal that is geometrically altered by the patients temporomandibular joint action and changes in head position
In another embodiment, a hypoallergenic UV cured acrylic shell hearing aid body (or similar material) is used, but the hearing aid body geometry for the right and left ear is modified by computer modeling to add two acoustic seal ring channels. The first channel is positioned near the receiver and face plate and the second near the transmitter. The channel depth is a fixed distance from the ear canal following the contour of the ear canal at the exact location of the acoustic seal ring. The location of the channels is determined for each ear and selected in the area where the ear canal geometry movement due to the patient's temporomandibular joint action and change in head position is minimal.
In yet another embodiment, two compliant acoustic solid material ring seals are used; these comprise an elastomer of about 3 to 55 durometer (Shore A); and they position the hard hearing aid body at the center of the ear canal and along the acoustic axis of the ear canal. This results in improved acoustic response as distortion resulting from transmitter and receiver movement is minimized.
In yet another embodiment, two compliant acoustic solid material ring seals are used, comprising an elastomer of about 3 to 55 durometer (Shore A) that provides acoustic sealing near the transmitter and the other near the receiver and face plate. This prevents acoustic feedback. This is a direct result of removing any portion of the shell that would interfere with the ear canal that is geometrically altered by the patient's temporomandibular joint action and changes in head position.
In yet another embodiment, two compliant acoustic solid material ring seals are used, comprising an elastomer of about 3 to 55 durometer (Shore A); these seals provide stable positioning of the receiver and transmitter in the ear canal, thus minimizing distorted acoustic response due to mandibular motion.
In yet another embodiment, two compliant acoustic solid material ring seals, comprising an elastomer of about 3 to 55 durometer (Shore A) provide true acoustic sealing and allow more acoustic power directed at the tympanic membrane without acoustic feedback.
In another embodiment, two compliant acoustic solid material ring seals, comprising an elastomer of about 3 to 55 durometer (Shore A), allow positioning of the transmitter in the sensitive bony portion of the ear canal. This greatly improves the acoustic performance of the hearing aid instrument.
In another embodiment, two compliant acoustic solid material ring seals, comprising an elastomer of about 3 to 55 durometer Shore A, allow positioning the transmitter near the sensitive bony portion of the ear canal. In some cases it is not possible to position the hearing aid instrument in the bony portion of the patient's ear canal.
In another embodiment, two compliant acoustic solid material ring seals, comprising an elastomer of about 3 to 55 durometer (Shore A), each have a different Shore A durometer. The acoustic ring seal near the face plate and the receiver have either a higher or lower Shore A durometer than the acoustic ring seal near the transmitter deep in the canal. The system can thus be finely tuned to the patient's special requirements.
In another embodiment, two compliant acoustic solid material ring seals, comprising an elastomer of about 3 to 55 durometer (Shore A), are preferably easily replaced by the hearing professional. This is necessary for both clinical reasons and for the resulting wear that will occur. This is caused by the many insertions and removals of the instrument from the ear canal.
In another embodiment, two compliant acoustic solid material ring seals, comprising an elastomer of about 3 to 55 durometer (Shore A), are preferably securely held and positioned on the hearing aid body by two close tolerance annular channels and by the elastic tension of the elastomer ring seals when assembled on the annular channels.
In yet another embodiment, two compliant acoustic solid material ring seals, comprising an elastomer of about 3 to 55 durometer (Shore A), are made from one or more soft, compliant materials. By way of illustration, some suitable compliant materials include silicone polymer, polyurethane and polymeric retarded recovery foam.
In another embodiment, two compliant acoustic solid material ring seals, comprising an elastomer of about 3 to 55 durometer (Shore A), have one or more different cross-sectional shapes. One preferred cross section is a quad type of seal with four lobes. This provides twice the acoustic sealing surface of a comparable standard circular cross section.
In another embodiment, two compliant acoustic solid material ring seals, comprising an elastomer of about 3 to 55 durometer (Shore A), have different combinations of cross sectional shapes on the same hearing aid body. The system can thus be finely tuned to the patient's special requirements.
In another embodiment, two compliant acoustic solid material ring seals, comprising an elastomer of about 3 to 55 durometer (Shore A), provide acoustic seals near the transmitter and near the receiver and face plate. The result is reduced power required for the transmitter and improved battery life.
In another embodiment, two compliant acoustic solid material ring seals, comprising an elastomer of about 3 to 55 durometer (Shore A), provide controlled vibration isolation of the hearing aid positioned in the ear canal This lowers the natural frequency of the hearing aid positioned in the ear canal.